1. Field of the Invention
The present invention relates generally to chain devices and, more particularly, to a chain device in which noise produced at the time of meshing engagement of the chain with the sprocket wheel is reduced by a buffer ring provided on one side of the sprocket wheel.
2. Description of Related Art
A chain, such as one used for power transmission on a motorcycle or the like and coupled to "drive" and "driven" sprocket wheels in mesh therewith, is normally passed around such sprocket wheels in a slack state and is suddenly brought into meshing engagement with the sprocket wheels as it is run therebetween. Therefore, each time the chain is forced into meshing engagement with each sprocket wheel, impact sounds consisting mainly of high frequency components are produced as a result of collision between the two metal parts. A generally known means for solving such chain noise problems makes use of the compressive deformation of rubber or the like for absorbing shocks at the time of meshing of the chain, and consequently wear problems are likely to arise. Particularly, when the buffer member formed of rubber or the like is provided on the drive sprocket wheel rather than the driven sprocket wheel by means of baking, premature wear will result due to great load conditions, which is a drawback from the standpoint of durability. Without such sacrifice of durability, no reliable noise prevention effect can be expected with such known means.
In order to afford a solution to the above problems, the present inventors have proposed a chain noise prevention device as disclosed in Japanese Utility Model Application No. 71829/1977 filed June 2, 1977, which corresponds to United States Patent Application Ser. No. 909,517 filed May 25, 1978 and entitled "CHAIN NOISE PREVENTING DEVICE." In such device, a buffer ring having an outer diameter greater than the inner-diameter dimension of a semicircular-shaped portion of the chain which is in mesh with a sprocket wheel is held on one side of the sprocket wheel by a retainer member secured to the same side of the sprocket wheel. With such construction, at the time of meshing engagement of the chain with the sprocket, a radially inner portion of each link of the chain is brought into engagement with the outer periphery of the buffer ring to alleviate the impact between the chain and sprocket wheel. In addition, the buffer ring is deformed at such time to absorb the impact energy, thereby further preventing the generation of impact sounds, and reducing noise.
The present invention provides improvements over the above-described proposed chain noise prevention device, so as to further promote noise prevention and to enhance the durability of the buffer ring.
Because the above-mentioned buffer ring has an outer diameter greater than the inner diameter of a semicircular-shaped portion of the chain which is in mesh with the sprocket wheel, with the meshing engagement between the chain and sprocket wheel the buffer ring restrained by the radially inner part of the semicircular chain portion is deformed into a substantially elliptical form and protrudes toward the non-restrained side. The buffer ring has a base formed of a plate spring member, so that at the time of such meshing engagement the restoring resilient force of the spring acts in the direction of the minor axis of the ellipse. The portion of the elliptically formed buffer ring traversing the minor axis thereof substantially coincides with a portion of the chain corresponding to the start of the meshing engagement between the chain and sprocket wheel at the time of forward or reverse running. Thus, the restoring resilient force of the buffer ring acts as a spring load upon the mesh start portion of the chain, with the buffer ring and chain engaging each other to produce a maximum contact pressure therebetween in such portion. Accordingly, if smooth engagement of the outer periphery of the buffer ring with the inner periphery of the semicircular chain portion can be obtained in such portion, it is possible to further reduce the chain noise compared with prior art means, and also to minimize wear of the buffer ring to enhance the durability thereof.